The calibration and test devices used in ophthalmological measuring systems are hereby also termed reference objects and particularly as so-called test eyes.
With certain technical and particularly medical devices, a recurring calibration and adjustment is necessary during the routine process in order to ensure the required quality, proper functioning, and safety of the devices. Thereby, the increasingly sought after enhancement of the measurement accuracy of technical devices is contradictory to the feasibility of the simple and reproducible accuracy of the calibration and test devices.
Users of ophthalmological instruments are often encouraged to attach calibration and test devices in predetermined intervals, and/or before measurements of the patient, to the instrument, measure said instrument and compare the obtained measurements with the presets. This applies particularly to devices for biometry, keratometry, topography of the eye, or also Scheimpflug cameras. Hereby, complex light structures, such as slices, rings, slits, or the like, must be projected, sometimes simultaneously, with large and/or very different angles onto the eye.
According to prior art, ophthalmological measuring systems for the determination of the biometric data of an eye as well as calibration and test devices for the verification of the functionality and the state of calibration in the form of test eyes are sufficiently known, whereby calibration and test devices in the form of scale representations or surface representations are hereby used.
In ophthalmology, the calibration and test devices in the form of test eyes are therefore measured, evaluated, and appropriately marked in advance with test standards. According to known prior art, the test eyes receive only an indicator in the form of numerical values or physical size indicator, readable by the user without technical means. Thereby, the data for the test eyes to be used are stored in some cases in the optical device. For the use of other than the stored test eyes, an appropriate adjustment of the software of the optical device is required.
In other optical devices said data are not stored. The operator of the optical device to be calibrated and/or adjusted is faced with the task of manually comparing the numerical values printed on the test eye with the measurements of the optical device during the measurement of the test eye. Empirically, this can lead to incorrect decisions in day-to-day usage due to lack of care. Said incorrect decisions inevitably result in faulty measurement results and can ultimately lead to misdiagnoses and even mistreatments. Incorrect decisions or confusions due to lack of care can, among others, also lead to significant problems in a connected discipline.
For example, DE 195 04 465 A1 describes a calibration and test device for optical eye length measurement devices, particularly for interferometric measurements. Hereby, transparent spheres with an approximate diameter of 16 mm and an approximate refractive index of 2 are utilized as calibration and test devices. As a result, the radius of curvature of the surface of the test body approximately corresponds to the cornea of the eye, so that the beam path in the measuring system, as with the measurement, runs in the natural eye. In a preferred embodiment, the test body exhibits a definedly reduced transmission in order to better adjust the transmission and/or reflectivity to the conditions in the eye. Through the change of the reflectivity of the coatings of the front and/or back of the test body and their transparency, different human eyes can be recreated.
A further calibration and test device for optical eye length measurement devices is described in DE 199 36 571 B4. It comprises two plano-convex lenses, which are arranged in the illumination beam path and aligned in opposite directions, and between which a neutral filter with a defined transmission is positioned. Herewith, a test body is provided that, despite its relatively simple design, is universally applicable for optical eye length measurement devices. For the reduction of unwanted reflections on the planar plate, the entire arrangement is used at an angle of between 10 and 20 degrees. Through the use of another gray filter or the variation of its thickness, additional test spheres can be dimensioned, which simulate various haze values due to eye cataract. Advantageously, a precise absorption can be set through a variation of the tilting in the beam path since a tilting of approximately five degrees represents a transmission correction of approximately 20-25%.
According to prior art, only solutions are known for the determination of the biometric data of an eye with ophthalmological measuring systems, wherein the necessary calibration and test devices are designed as separate optical elements and utilized at regular intervals for testing the functionality and the state of calibration.
A number of known methods and measurement devices exist for the determination of the biometric data of an eye. For example, prior to a surgical procedure for exchanging the eye lens in case of a lens opacification (cataract), it is necessary to determine various biometric parameters of the eye. In order to ensure eyesight as optimal as possible after surgery, it is necessary to determine said parameters with sufficiently great accuracy. The selection of a suitable replacement lens based on the determined measurements takes place by use of established formulas and calculation methods.
The most important parameters to be determined are, among others, axial length (distance to the retina), corneal curvature and refractive power as well as the length of the anterior chamber (distance to the eye lens). These measurements can be obtained successively with different ophthalmological instruments or with the help of specially optimized biometric measurement devices.
In addition to ultrasound measurement devices, optical measurement devices on the basis of short-coherence interferometry methods have particularly prevailed for the determination of said parameters. With these methods based on short-coherence interferometry, depth profiles or two-dimensional depth cross sections of scattering potentials, particularly of scatterings at structural transitions, are depicted. Hereby, the so-called OCDR (optical coherence domain reflectometry) method and the so-called OCT (optical coherence tomography) have prevailed as short-coherent measurement methods.
With OCDR, temporally incoherent light is used with the help of an interferometer for the acquisition of depth profiles on reflective and scattering structures, and distance measurements based thereupon. In addition, as described in U.S. Pat. No. 5,321,501, imaging is realized on the reflective and/or scattering structures with OCT by means of a beam deflection. Such systems as well as Scheimpflug camera systems, e.g., are suited for obtaining biometric data from image information, such as the dimensions of the anterior chamber of the eye, needed, e.g., for the adjustment of phakic intraocular lenses.
U.S. Pat. No. 7,322,699 B2 describes a combination device for the non-contact determination of biometric data, such as axis length, anterior chamber depth as well as corneal curvature. Based on the measurement of the required data, it is possible with the described solution to perform everything from the calculation to the selection of the intraocular lens IOL to be implanted with only one device. As a result, increased stress on the patient due to multiple placings and measurements with various devices as well as data losses or data corruptions through transfer of the measurements between various devices can be avoided.
A combination device for non-contact determination of axis length, anterior chamber depth as well as corneal curvature of the eye as well as the calculation and selection of an intraocular lens IOL to be implanted, is described in DE 198 57 001 A1. The measured variables, which are also important for the selection of an intraocular lens IOL to be implanted, must be determined particularly prior to cataract surgery but also during the follow-up of school myopia and aniseikonia determination. The determined measured variables are inserted in formulas which calculate the optical effect of the IOL. Depending on the type of device to be used, various errors may occur which influence the selection of the IOL.
Until now it has been customary in the clinical practice to measure said variables by means of at least two devices (e.g., ultrasound a-scan and automatic keratometer). Since the computation of the IOL can now take place by means of a device arrangement, data losses or data corruptions are also emitted during the transfer of the measurements from various devices to the computer which effects the computation of the IOL. The IOLMaster® from Carl Zeiss Meditec AG, based on a short-coherent method, represents an optical measurement device in accordance with the described solution principle.
Usually, an included test sphere is to be measured regularly for the calibration and/or verification of the functionality measuring functions of such devices.
Thereto, e.g., a holder with a test sphere is inserted into holes positioned next to the chin rest. The test spheres display the respective nominal values and tolerances which serve the verification of the state of calibration. The device should only be activated when the measurements provide results which correspond with the nominal values on the test sphere within the also indicated tolerances. After the completed measurement, the test spheres are to be removed and safely stored in order to avoid damage and/or contamination.
US 2007/0291277 A1 describes an ophthalmological system which comprises an optical coherence tomography system (OCT), a fundus detection system, an iris detection system, a motorized chin rest, internal test structures, and a fixation marker unit. Thereby, the internal test structures, which are essentially designed as spaced surfaces as well as crosshairs, or as horizontal and/or vertical beam structures, are provided for the verification of individual functionalities. However, said internal test structures only allow for internal functional tests and calibrations of the OCT system (optical coherent tomography) and/or for the LSLO system (line scanning laser ophthalmoscope) used for fundus detection but, particularly, they do not allow for those with regard to all optical components on the entire beam path to and from the patient's eye. Therefore, in addition to the internal test structure, US 2007/0291277 A1 still contains the description of a conventional test eye which is solely designed for calibrations and, in addition, has to be attached manually.
The document WO 2006/128596 A1 describes in this context a microkeratome for application in ophthalmology, particularly for the LASIK method. With the so-called LASIK method, the cornea of an eye is cut laterally to the optical axis, producing a corneal lid, also called flap. After the flap is folded back, the ablation of the underlying stroma of the cornea is effected. This way, the cornea can be shaped in accordance with the respective defective vision. After the completed correction, the flap is returned to its original position. Thereby, the flap attaches itself on its own and coalesces without having to be sutured. Microkeratomes are used for the incision in the cornea, which, as a rule, contain replacement components to be chosen by the operator in dependence of the pending surgery. Such replacement components are particularly the cutting head and the suction ring. Different replacement components have different effects on the execution of the surgical procedure. In the solution described here, the replacement components each exhibit an identification which describes the identifying features of the respective replacement components. The identifications can be read and utilized with a reading device. The identification data can, e.g., be directly displayed for the operator on a screen and/or used as basis for a calculation for the control of the microkeratome system. The system described hereto, barcodes are preferably provided for the identification of the replacement components. This solution described hereto implies the use of an additional reading device in the form of an appropriate barcode reader and is neither designed for the calibration and/or adjustment of a device nor suited for such tasks.